1. Field of the Invention
This invention relates to feeding metal logs to a heating furnace. In one of its aspects, the invention relates to a method of heating metal logs to an elevated temperature wherein the logs are fed seriatim to an elongated heating zone. In another of its aspects, the invention relates to an apparatus for heating metal logs in an elongated heating furnace wherein the logs are pushed seriatim end to end into a heating furnace. In still another of its aspects, the invention relates to an apparatus for feeding metal logs to an elongated heating furnace.
2. State of the Prior Art
In aluminum extrusion plants, aluminum billets are heated to an elevated temperature and are extruded into formed shapes. The billets are generally of a size selected to produce the shapes of a given length. Thus, in order to minimize scrap, the size of the billet is selected to meet the needs of the shape and length of the extruded products. For this purpose, billets of different sizes and different compositions may be needed.
It has become the practice in such extrusion plants to inventory logs of approximately 12-20 feet, to heat the logs to an elevated temperature and to cut the logs to a predetermined size just prior to the use of billets in the extrusion press. One type of furnace used to heat logs to elevated temperature has an elongated heating chamber with an entrance opening and an exit opening at opposite ends. A pusher table is positioned adjacent the entrance opening of the furnace and a conveyor, usually a roller conveyor, extends along the pusher table, through the entrance end of the furnace and through the exit end of the furnace. A log dispenser is positioned adjacent the pusher table for dispensing logs seriatim onto the conveyor at the pusher table. A pusher mechanism is mounted for movement along the conveyor between opposite ends of the pusher table to push the logs along the conveyor in a log train into and through the furnace. The log train has a leading log on the conveyor at an exit opening in the furnace and a lagging log which may be partially or wholly supported by the conveyor at the pusher table. A shear press is positioned adjacent the exit opening of the furnace for cutting the logs into billets.
When a billet is required at the shear press, the pusher pushes on the lagging end of the lagging log to push the leading log out of the exit end of the furnace and pass the shear press a distance equal to the desired size of the billet. The shear press is operated to cut the billet to a particular length. The billet is removed and sent to the extrusion press. A reverse pusher then pushes the leading log back into the furnace for continued heating. Thus, the log train reciprocates back and forth in the furnace and into and out of both the entrance opening and exit opening of the furnace.
In this process, there comes a time when the pusher on the pusher table reaches the end of its track at the entrance opening of the furnace. If this point is reached when the log train is being pushed to the shear press, the pusher mechanism must stop and retract, allow a second log to be positioned on the conveyor and then continue the pushing operation until the leading log reaches the proper position at the shear press. This operation is known as "double clutching." The double clutching operation results in a slowdown in the extrusion cycle since some appreciable time expires between the time the pusher can retract to an opposite end of the pusher table and a new log can be dispensed and brought up to the log train. All of the extrusion equipment and runout equipment is waiting while this double clutching operation takes place. This operation decreases the efficiency of an extrusion plant.
In order to overcome this problem, the pusher table length has been extended and the log-dispensing mechanism has been spaced a farther distance from the entrance opening of the furnace. Typically, the distance between the entrance opening of the furnace and the leading edge of the logs in the log dispenser is equal to the maximum cut length of the billet, plus the distance from the shear press to the shear line, plus the distance from the furnace entrance and to the maximum forward position of the pusher and plus a small tolerance. This distance is perhaps 5-6 feet. With this construction, a new log can be added to the log train during the period of time that the leading log has been returned to the furnace without interfering with the pusher mechanism. When the pusher reaches a predetermined position close to the furnace during a billet-shearing interval, the pusher mechanism can be retracted and a new log added to the pusher table conveyor without interfering with the lagging log in the log train.
The problem with the spacing solution is that it adds 5-6 feet to the length of the furnace equipment. Plant space is costly and thus the equipment adds additional cost on an ongoing basis to the plant operation. However, in some case, there is simply not enough room in the plant to put in this additional-length equipment.